1. Field of the Invention
The present invention relates to an intermediate transfer member and an image formation apparatus using the same. More particularly, the present invention pertains to an intermediate transfer member which is employed in an electrophotographic image formation apparatus such as copying machinery, facsimile machinery and laser printers, and which prevents toner fixing, or improves the behavior of repeated deformation due to contact with a toner, a photosensitive body, a secondary transfer member, a cleaning member and the like, and thus enhances its durability; and an image formation apparatus which is equipped with said intermediate transfer member.
2. Description of the Background
In the conventional electrophotographic image formation apparatus such as copying machinery, facsimile machinery and laser printers, printed images have heretofore been obtained by a method comprising the steps of allowing the surface of a photosensitive body, that is, an image formation body to be charged uniformly; projecting an image from an optical system on the photosensitive body to remove the charge of the light-irradiated portion, thereby forming an electrostatic latent image; then supplying the resultant electrostatic latent image with a toner from a developing roller or the like to form a toner image by the electrostatic adhesion; transferring the resultant toner image to a recording medium such as paper by means of a transfer roller or the like; and heat fixing said image by the use of a fixing roller or the like so as to obtain the objective printed image.
Likewise in color printers and color copying machinery, printing is carried out basically in accordance with the above mentioned process. In the case of color printing, since the color tone is reproduced by the use of four toners having different colors including magenta, yellow, cyan and black, there is required a step for the purpose of obtaining the desired color tone by superimposing the aforesaid toners at a prescribed ratio. Thus several proposals have been made on a method for putting the above-mentioned step into practice.
There is available as a first system, a multiple development system in which at the time of visualizing an electrostatic latent image by supplying a photosensitive body with a toner as is the case with black and white printing, development is carried out by superimposing in turn, the aforesaid four toners having different colors including magenta, yellow, cyan and black so as to form colored toner images on the photosensitive body. Said system, although being capable of constituting a development unit in a comparatively compact manner, involves a problem that the gradation is extremely difficult to control, thus making it impossible to obtain a high quality image.
There is also available as a second system, a tandem system in which four photosensitive bodies are equipped; the latent images of the respective photosensitive bodies are developed with toners having different colors including magenta, yellow, cyan and black, respectively, so as to form four toner images with magenta, yellow, cyan and black, respectively; the photosensitive bodies on which these toner images are formed are arranged in a row and are consecutively transferred to a recording medium such as paper; and said images thus transferred are superimposed on the recording medium so as to reproduce color images. However, although favorable images are obtained, the above-mentioned system brings about a state in which the four photosensitive bodies and the electrically charging mechanism and development mechanism that are installed per each photosensitive body, are arranged in a row, whereby the development unit is made unfavorably large-sized and expensive.
There is further available as a third system, a transfer drum system in which a recording medium such as paper is wound around a transfer drum; said drum is rotated four times, while toners of magenta, yellow, cyan and black, respectively, on the photosensitive body are consecutively transferred to a recording medium such as paper per each one rotation so as to reproduce color images. However, although comparatively high quality images are obtained, the above-mentioned system involves the problem that in the case where a recording medium is a thick sheet of paper such as a postcard, said medium is difficult to wind around a transfer drum, thereby unfavorably limiting the kind of the recording medium to be used.
As a countermeasure against the foregoing multiple development system, tandem system and transfer system, there is proposed an intermediate transfer system as a system capable of producing a favorable quality of image without necessitating a large-sized apparatus in particular or specifically restricting the kind of a recording medium.
The intermediate transfer system is a system which comprises equipping the system with an intermediate transfer member made up of a drum or a belt which once transfers and retains the toner images on a photosensitive body to and on itself; consecutively transferring to said intermediate transfer member, the four color images on the photosensitive body, that is, four toner images with magenta, yellow, cyan and black, respectively so as to form color toner images on said intermediate transfer member; and transferring the resultant color toner image to a recording medium such as paper. The above-mentioned intermediate transfer system is capable of producing high quality images, since the system regulates the gradation by superimposing the four color toner images, dispenses with a large-sized apparatus in particular, since there is no need to arrange photosensitive bodies in a row, differing from the tandem system, and further does not restrict the kind of a recording medium, since there is no need to wind a recording medium on a drum, differing from the transfer drum system.
However, with respect to the above-mentioned intermediate transfer system, the intermediate transfer member is liable to raise a problem of durability, since said member comes in contact with a photosensitive body, a secondary transfer member, a cleaning member and the like.
It is known that the durability of the intermediate transfer member is greatly influenced by a slight deformation thereof due to contact thereof with the residual toner, the photosensitive body, the secondary transfer member, the cleaning member and the like. That is to say, the toner which is primarily transferred from the photosensitive body and is retained on the surface of the intermediate transfer member, must be secondarily transferred to a recording medium such as paper in the next step. In the case where, however, by reason of poor secondary transfer or poor cleaning as the matter of tact, part of the toner is left on the intermediate transfer member, and is gradually embedded on the surface of the intermediate transfer member to cause fixing. The toner, if once embedded thereon, begins to be deposited acceleratingly and appears on an image as defective points. Inherently, it is the fundamental measure to enhance the transfer efficiency as well as cleaning efficiency so as to prevent the toner from remaining on the intermediate transfer member. Nevertheless, with the state of the art it is difficult to remove 100% of the remaining toner.
In addition, the surface of the intermediate transfer member is subjected to repeated deformation in a slight depth owing to the contact of said member with the photosensitive body, the secondary transfer member, the cleaning member and the like, whereby there are caused, though slight, change in the surface configuration of the member, localized distortion of an image, variation in the aspect ratio of an image and the like.
By decreasing the pressure of the contact of the intermediate transfer member with the photosensitive body, the secondary transfer member, and the cleaning member, it is made possible to decrease the repeated deformation due to the contact with the aforesaid members, but such decrease in pressure deteriorates the efficiencies of the primary and secondary transfers, which are the inherent functions of the intermediate transfer member.
In such circumstances, an attempt is made to coat the surface of the intermediate transfer member with a fluorine based material excellent in antifouling properties and sliding properties in order to prevent the residual toner from fixing to the surface of the intermediate transfer member and at the same time, decrease the friction between said member and the photosensitive body, the secondary transfer member, and the cleaning member. It is the present status that said attempt, although being effective to some extent, results in failure to assure sufficient durability.